1. Field of the Invention
The present invention relates to a controller for controlling lenses. More particularly, the present invention relates to a lens controller which has as a photographing lens a zooming optical system composed of a focusing lens group and a zooming lens group respectively disposed on the same optical axis and performs focusing adjustment and operation by driving the focusing lens group and performs a zooming operation for changing the focal distance of the lens group by driving the zooming lens group.
2. Discussion of the Background
With respect to a zooming lens, there is no shift of an image forming position(the so-called focusing movement or shift) even when the zooming operation is performed. Accordingly, it is not necessary to perform the focusing adjustment in every zooming operation. However, an open diaphragm F number is small in comparison with a single focusing lens. For example, a certain skill is required to perform the focusing adjustment or operation by a single-lens reflex type finder. Recently, the cameras have been automatically focused and thereby this problem has been solved. Thus, the function of the zooming lens itself can be fulfilled so that an operator can concentrate on only the determination of composition along the intention of taking a photograph, thereby greatly improving the operability.
In general, the focusing operation of the zooming lens is performed by moving a focusing lens group disposed in a portion of a zooming optical system. In the case of the zooming lens, the moving amount of the focusing lens group is approximately the same with respect to the same distance between the lens and a photographed object in the entire zooming region, which is called an equivalent amount movement in the following description. Accordingly, a scale for indicating the distance of the photographed object is additionally disposed in a moving member(distance ring) of the focusing lens group. Further, an index is additionally disposed in a fixed ring adjacent to this scale. By such a simple construction, the distance between the lens and the photographed object can be indicated, and it is not necessary to change the scale for the distance of the photographed object in accordance with the zooming operation.
However, in the zooming lenses of an inner focusing system and a rear focusing system, when an optical design is performed under the condition of realizing the above-mentioned equivalent amount movement, the construction of the lens is complicated and the moving amount(the drawing-out amount) of the focusing lens group is excessively large on the wide angle side thereof. These situations depend on the construction of the lenses of the zooming optical system.
Further, by such a construction, the outer diameter of the lens becomes large and therefore the lens and the body tube become heavy.
The operability of the zooming lens is improved by combining this lens with the auto focusing function. However, the condition of the above equivalent amount movement provided for the zooming lens is required so that it is still difficult to make the lens controller compact and reduce the cost of the lens controller.
The same applicant as this applicant has therefore proposed a varifocal lens controller for solving the above-mentioned problems as Japanese application No. 62-013345.
In this prior application, a zooming optical system is composed of a zooming lens group and a focusing lens group arranged on the same optical axis. The focusing lens group of the zooming optical system is set in a focusing position from a proximate position to an infinite position on the optical axis corresponding to the distance of a photographed object from the proximate position to the infinite position. Thereafter, the focal distance of the entire zooming optical system is changed by the zooming lens group from an arbitrary first focal distance to a second focal distance between the shortest and longest focal distances, thereby shifting the image forming position with respect to the same photographed object. Such a varifocal lens controller comprises focal distance detecting means for detecting the above focal distance of the entire zooming optical system; focusing lens group position detecting means for detecting the position of the focusing lens group on the above optical axis; maximum drawing-out amount calculating means for receiving an output of the focal distance detecting means and calculating the drawing-out amount of the focusing lens group from the infinite position to the proximate position with respect to the above focal distance; and proportional constant calculating means for receiving outputs of the maximum drawing-out amount calculating means and the focusing lens group position detecting means and calculating a ratio of these outputs. The varifocal lens controller further comprises focusing correction calculating means for receiving outputs of the proportional constant calculating means, the maximum drawing-out amount calculating means and the focusing lens group position detecting means and calculating, as a correction value, a shifting amount of the image forming position from the said focal position caused by the change in focal distance of the entire zooming optical system; focusing drive means for driving the above focusing lens group; moving amount monitoring means for generating a signal corresponding to the moving amount of the focal lens group; and focusing control means for receiving outputs of the moving amount monitoring means and the focusing correction calculating means and controlling the focusing lens group to move this lens group to the above focal position. The varifocal lens controller further comprises zooming drive means for driving the above zooming lens group; and zooming control means for receiving a start signal from starting means separately disposed and controlling the above zooming drive means. The varifocal lens controller is thus constructed to automatically correct the shift of the image forming position caused by the change in focal distance of the entire zooming optical system.
On the other hand, many cameras have recently been electronized and automatically driven. In such cameras, various kinds of operations are automatically performed by the so-called one touch operation (or single operation). In such a situation, the camera body tends to be made compact and the number of operating switches is necessarily increased as the number of functions of cameras is variously increased. It is natural and rational that the operability of the operating switches is considered with the size of the man's fingers as a reference. Namely, in the case of a push-buttom switch for example, it becomes easy for an operator to push the switch as the area for an operating face pushed by an operator's finger is increased. However, as mentioned above, the surface of the camera body has a limited area. To solve this problem, a technique for corresponding one operating switch to a plurality of operations has already been known.
For example, in a lens controller, an UP/DN switch for selecting the zooming direction is disposed to change the focal distance of the zooming lens on the longer focal distance side(telescopic side) or the shorter focal distance side(wide side). The lens controller further has an F/Z switch for manually selecting the focusing operation and the zooming operation, and an A/M switch for selecting whether the focusing operation is performed automatically or manually. The lens controller further has a ZG/MG switch for selecting whether the zooming lens is set to take a macroscopic photograph or is returned to a zooming region. The focusing operation is selected by the F/Z switch in the lens controller mentioned above. In such a lens controller, a switch for indicating the focusing direction is insufficient. In such a case, as is well known, the lens controller is constructed such that the switching operation of the above UP/DN switch corresponds to two operations, and the F/Z switch constructs a switch for indicating the zooming direction when the F/Z switch selects the zooming operation and constructs a switch for indicating the focusing direction when the F/Z switch selects the focusing operation.
In accordance with the invention of the prior application constructed above, the lens optical system itself has a very simple construction and is compact, and light and cheap. The entire lens controller is similarly compact, and light and cheap. Further, even when the focal distance of the entire lens optical system is changed by moving the zooming lens group from the arbitrary first focal position to the second focal position, the shift of the image forming position peculiar to the varifocal lens can be immediately corrected to hold the focusing state. Accordingly, such a lens controller substantially provides a lens system equivalent to the zooming lens when this lens controller is used.
However, in the varifocal lens in accordance with the invention of the prior application, the condition of the above equivalent amount movement is removed therefrom. Therefore, when the focal distance is changed with respect to the photographed object separated by the same distance, the drawing-out amount of the focusing lens group is changed to perform the focusing operation. Accordingly, when the zooming lens group is driven to perform the zooming operation for changing the focal distance, the shift of the image forming position caused by this zooming operation must be corrected by the above focusing operation. The correcting amount for correcting this shift is changed by the focal distance as mentioned above, but the rate of this change is further changed by the distance of the photographed object. For example, in comparison with the zooming time required to perform the zooming operation from the longest focal distance to the shortest focal distance, this zooming time is short in the case of the distance of the photographed object providing a small rate of the above change and is long in the case of the distance of the photographed object providing a large rate of the above change. Accordingly, there is a problem that the zooming time is not uniform by the distance of the photographed object with respect to the same changing amount of the focal distance.
In a certain case, in accordance with the construction of the varifocal lens, when the focal distance of the entire zooming optical system is changed from the shortest focal distance to the longest focal distance, the focusing position in the infinite position(.infin. position) is not changed and the focusing position in the proximate position is changed so as to move away from the infinite position. In such a case, when the operation of the focusing lens group is controlled while the zooming lens group is moved to perform the zooming operation from the long focal point side to the short focal point side, or conversely, when the zooming operation is performed onto the side of the long focal point, the focusing lens group hits against a positioning member such as a stopper, etc., in the infinite position and the proximate position. Therefore, the focusing lens group cannot be moved and controlled, and the load of a drive motor is excessively increased, thereby causing a new problem.
Further, the following problems are caused in the case in which the operation of the UP/DN switch corresponds to the two operations and the F/Z switch constructs a switch for indicating the zooming direction when the F/Z switch selects the zooming operation, and constructs a switch for indicating the focusing direction when the F/Z switch selects the focusing operation.
In the following description, it is assumed that the composition(angle of view) has been completely determined and the F/Z switch is switched onto the side of the focusing operation. Further, it is assumed that the F/Z switch has been switched in error onto the side of the zooming operation while the UP/DN switch is operated to perform the focusing operation in accordance with the above-mentioned composition. In such a case, the UP/DN switch fulfills an original function of a switch for indicating the zooming direction so that the zooming operation is started and thereby the composition already determined is changed.
In a normal macro mode for fixing the focal distance of the zooming lens to a predetermined focal distance or magnification within a macro region by the ZG/MG switch, this magnification should not be changed after this fixing operation so that the zooming operation is inhibited and only the focusing operation is allowed in accordance with the general construction of the lens controller. However, in such a construction, when the F/Z switch is set onto the side of the zooming operation, the focusing operation by the UP/DN switch cannot be performed and the zooming operation also cannot be performed since the zooming operation is inhibited as mentioned above. Therefore, a beginner, who does not use such a camera so often, gets confused in such a situation. Further, it takes time to perform a suitable operation in such a situation even in the case of an operator who often uses the camera. Therefore, an important shutter chance of the camera is lost in a certain case.
When the A/Z switch is set onto the auto focusing side, the manually focusing operation is naturally inhibited and only the zooming operation is allowed in accordance with the general construction of the lens controller. However, in such a construction, when the F/Z switch is set onto the side of the manually focusing operation, the zooming operation cannot be naturally performed by the UP/DN switch and the manually focusing operation also cannot be performed since the manually focusing operation is inhibited as mentioned above. Therefore, the operator or user of the camera gets confused and a suitable operation is delayed in such a situation.